This specification relates to semantic document analysis.
When a webpage's content changes, some of the changes are relevant to what an end user would believe is the main content of the webpage. Other updates to the webpage may be irrelevant to what an end user would believe is the main content of the webpage, e.g. a change in an advertisement. Some changes to a webpage can be detected by structural analysis of the document, such as changes in the Document Object Model (DOM) structure and detection of new text with filtering done by boilerplate detection.